Various strength training devices and systems have been developed to improve health and fitness, such as those described in U.S. Patent Publication No. 2004/0005968 to Crawford et al. (“Crawford”). Crawford discloses a dumbbell that includes a handle having a grip and at least one end. An inner plate is mounted on the handle adjacent the grip in a fixed rotational orientation. A support plate is rotationally mounted on the handle adjacent the inner plate. At least one collar is rotationally mounted on the handle adjacent the support plate and rotationally fixed with the support plate. A selector knob is rotationally mounted on the handle adjacent the at least one collar, and rotationally fixed to the collar. A weight plate is removably mounted on the handle adjacent the at least one collar by rotating the selector knob, which in turn rotates the at least one collar into engagement with the weight plate. In addition, various other devices and/or dumbbells have been devised in an effort to make strength training convenient and accessible.
In addition, other exercise devices include those in U.S. Patent Publication No. 2009/0186748, U.S. Patent Publication No. 2006/0211550, U.S. Patent Publication No. 2008/0039299, U.S. Patent Publication No. 2010/0035736, U.S. Pat. Nos. 5,123,885, 5,637,064, 5,769,762, 5,779,604, 5,839,997, 5,971,899, 6,149,558, 6,186,928, 6,196,952, 6,228,003, 6,261,022, 6,402,666, 6,416,446, 6,500,101, 6,540,650, 6,669,606, 6,679,816, 6,719,674, 6,749,547, D500,820, 6,855,097, 6,872,173, 6,899,661, 6,997,856, 7,066,867, 7,077,791, 7,261,678, and 7,534,199.